2003 NB TDI Glow Plug Relay?

I have two NB TDI's a '98 & '03 both Man trans.
The '03 developed a cold start problem this summer at warm ambient temps. Had one bad glow plug code so I changed them all w/ new. Still hard starting but if the temp sensor on the head is un-plugged glow plugs come on and starts right up. So I replaced the Temp sensor. No change. Changed fuel filter looking for a air leak problem.
Thought I'd switch the GP relay between the two and the '03 doesn't have one in the #10 relay spot, Started looking and there seem to be quite a few diffs ( no Map or 2nd temp sensor in the coolant line) it's an ALH, but seems to have some of the features of the BEW. The Bently Man doesn't show this from what I've been able to find (I have a newer one that covers the wife's '08 gasser). This morning, temp out 21 deg. glow plugs came on car started right up so only happens at warm ambient. But, I'm still a bit stumped as to where the GP Relay is. Any thoughts?

On the '02 and '03 ALHs, the GP relay should be in the area where the winshield wiper mechanism operates. The GP relay in the 02s going forward is a solid state relay. The GP relay in older TDIs is a mechanical relay and is located in the usual spot for it that you found empty. They're not compatible so you can't simply swap the two.

Where is your injection timing set at and when was the timing belt last changed and who did the work? Retarded injection timing will contribute to hard cold starts in cool weather where the engine is cold but not cold enough yet for the ECU to operate the GP system. As the weather gets colder, the hard starting behavior may go away or be less noticeable due to the enging getting glowplug use before a cold start.

I suspect the injection timing needs to be looked at.

Good luck and Welcome to TDIclub.

TDI Timing

Thanks for the reply,

My '98 consistantly gets better mpg than the '03 so, as an experiment a few weeks ago, I set the timing just above the green line to see if I could enhance the MPG (it worked). But, it had no effect on the warm start issue that began months earlier this spring. You are right, that now the ambient is dropping the GP cycle is working making the start easier. I also had an intermittant surge condition at speed along with a constant acceleration lag which repacing the N75 fixed.
The timing belt has not been replaced as far as I know, I bought the car w/ 70K mi. and just went over 100k so it's on my list but I checked a week ago and the belt looks good.
Just recieved the Snap-on compression adapter so I'm going to rule that out this week.
I do my own work on the cars, trucks, tractors and farm equip. here. It takes time but I work cheap
Any other thoughts or advise would be much appreciated.
Thanks, MAtt Williams